The present invention is concerned with a mask to be worn over a person's nose and mouth for the purpose of effecting the countercurrent exchange of heat and humidity to diminish body losses of same in severe environments.
The known prior art discloses various types of cold weather face masks which are primarily to protect the face from cold air and which only incidentally provide any pre-heating of inhaled air. For example, U.S. Pat. Nos. 3,768,100 and 4,300,240 disclose cold weather masks where respiration causes intake and exhaust air to pass through a layer of permeable material. U.S. Pat. No. 2,344,920 discloses the objective of routing intake air through receptacles, filled with some type of filtering material, and thence through tubes passing through an internal chamber of the mask to pre-heat the intake air and subsequently mixing said air with exhaled air in a common chamber. Such an arrangement encounters the disadvantage of minimal pre-heating and a sizable chamber into which exhaled air is discharged resulting in a portion of same being re-inhaled by the mask wearer. This reference, while pre-heating fresh air is considered, fails to disclose a mask concept utilizing a countercurrent exchange medium.
U.S. Pat. No. 2,909,782 discloses a cold weather mask wherein breathing results in inhaled and exhaled air passing through a single layer of coarse fabric.
With attention again to U.S. Pat. No. 3,768,100 the same discloses an "oronasal barrier" of air permeable material removably attached to a cold weather mask which has a stated purpose of maintaining inhaled air above ambient temperatures but makes no provision for incorporation of a medium effecting countercurrent exchange.